With the establishment of satellites--such as the LANDSAT satellite--there has been an increased recognition of the value of making observations of the earth's surface using equipment which employs thermal imaging techniques. Already, thermal imaging has been proposed for water pollution studies, forest fire detection and damage assessment, location of underground springs, obtaining an inventory of forest, mountain and agricultural lands, monitoring the ripening of wheat and other crops, and observing fishery and tidal movements. More recently, it has been appreciated that further information can be obtained using multi-band spectral analysis (that is, the technique of simultaneously observing an object in several regions of the electromagnetic spectrum), especially if that analysis can be performed on images obtained from low-level aircraft observations.
It is well known that low-flying aircraft often experience substantial turbulence. Consequently, if observations are to be made from low-flying aircraft (especially from light aircraft) using a scanning arrangement such as a rotating mirror, and maximum information is to be obtained from those observations, then perturbations of the scanning process due to roll, pitch and yaw of the aircraft must be compensated.
When making observations from a large aircraft, the effects of roll, pitch and yaw have been eliminated or substantially reduced by mounting the equipment carried in the aircraft on a stabilised platform. However, the use of a stabilised platform in a light aircraft imposes a substantial weight burden and also (because it is necessary to maintain stabilising gyroscopes in action) a substantial power burden.